I would add the nuance that "maintain" requires some effort as opposed to "preserve". For example, if you "maintain the appearance of a building", you would be actively engaged in restoration whereas "preserve" would imply that you're keeping exterior factors from altering the appearance of the building. Best wishes!

The words are similar in meaning and can be used interchangeably but I'm going to say that "maintain" is used more for physical things and "preserve" for biological things.

An example might be I lift weights to maintain my muscle mass. I preserve the fish i bought by keeping it in the freezer.